ps3_2010 - STAT 203 PROBLEM SET 3(1 An economist studying...

STAT 203 PROBLEM SET 3 (1) An economist studying the relation between household electricity consumption ( Y ) and number of rooms in the home ( X ) employed linear regression model and obtained residuals listed in ±le Electric-ityConsumption.txt . Plot the residuals versus X . What problem appears to be present here? Might a transformation alleviate this problem? (2) RABE Problem 7.4. (3) This problem uses data from a study of computer-assisted learning by 12 students, showing the total number of responses in completing a lesson ( X ) and the cost of computer time ( Y , in cents). (a) Fit a linear regression function by ordinary least squares. Ob-tain the residuals, and plot the residuals against X . What does the residual plot suggest? (b) Plot the absolute values of the residuals against X . What does this plot suggest about the relation between the standard devi-ation of the error term and X ? (c) Estimate the standard deviation function by regressing the ab-

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